Changing a battery in a modern car
Today's cars are full of computers that rely on a steady power supply. That means replacing the battery isn't always as simple as undoing two clamps. Done the wrong way, it can cause problems that are expensive to fix.
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Check your owner's manual, then use the right cable order.
A guide only. Your exact vehicle decides what's needed, so check your owner's manual or ask us.
What can go wrong, and the fix
Cutting the power, even for a few minutes, can cause these problems.
The right way to swap a battery
There are two ways to do it, and your car maker decides which one your car needs. In both, the right cable order reduces the risk of sparks and short circuits. The diagrams show the general order. Your car maker's instructions always come first.
Path 1 · Full disconnection
Path 2 · With backup power
Only where your car maker allows it, using the equipment and connection points they specify. Jump-start posts alone don't mean it's allowed.
With backup power connected, the detached red (+) cable stays live. Insulate it securely so it can't touch any metalwork. After fitting, many of these cars need a BMS reset, battery registration or coding with a diagnostic tool so the car charges the new battery correctly. The memory saver doesn't do this. That's usually a shop job. Where required and supported, the applicable procedure is included with your Battery24 battery replacement.
Path 1 · Full disconnection: step by step
Check your owner's manual or the maker's procedure. Some cars need the ignition off for a set time, or doors and windows set a certain way, before the battery is disconnected. Note which side the positive (+) and negative (−) terminals are on.
Remove the negative (−) cable first, then the positive (+), and then the hold-down clamp. Use two spanners, one on the nut and one on the bolt, so you don't twist the terminal and crack its seal.
Check the new battery is the right size, type (for example EFB or AGM) and layout. Clean the tray and the outside of the cable clamps. For heavy corrosion, wear gloves and eye protection and use one tablespoon of bicarbonate of soda in a litre of warm water on the external clamps and tray only. Keep the solution out of the battery vents, and catch the runoff with a cloth or container so it doesn't drain away. Fit the battery the same way round, secure the hold-down so it can't move, and reconnect the vent pipe if your battery has one.
Connect the positive (+) cable first, then the negative (−). Tighten each clamp to the maker's specification. Never hammer a clamp on, because this can break the terminal inside the battery. Finish with a thin coat of petroleum jelly (not grease) to prevent corrosion.
Some cars need settings, windows or steering relearned, or a BMS reset, battery registration or coding. Follow your car's requirements. A diagnostic scan on its own doesn't restore lost settings, and faults shouldn't simply be cleared.
Path 2 · With backup power: step by step
Only use backup power if your car maker allows it. Use a regulated, fused battery-support supply, not an ordinary charger or a jump starter on boost mode. Connect it only at the points the maker specifies. Jump-start posts on their own don't mean it's allowed.
A light on the backup unit doesn't prove the car is being powered. Some accessory sockets switch off with the ignition, so don't confuse them with the diagnostic (OBD) port, and don't switch the ignition on to make it work. Opening a door can wake the car's systems and overload a small unit. Never fit a bigger fuse or bypass it.
Remove the negative (−) cable first and tuck it away so it can't touch the battery or the terminal. Use two spanners so you don't twist the terminal.
Remove the positive (+) cable, then the hold-down clamp. With backup connected, this cable is still live. Insulate it securely so it can't touch any metalwork.
Check the size, type (usually EFB or AGM) and layout match. Fit it the same way round, secure the hold-down and reconnect the vent pipe if there is one.
Connect the positive (+) cable first, then the negative (−). Tighten each clamp to the maker's specification. Never hammer a clamp on.
Disconnect the backup supply only once both cables are tight. Many of these cars then need a BMS reset, battery registration or coding with a diagnostic tool, and some settings relearned. The backup supply doesn't do this. A scan on its own doesn't restore lost settings, and faults shouldn't simply be cleared. That's usually a shop job. Where required and supported, the applicable procedure is included with your Battery24 battery replacement.
This is general guidance for the 12 V battery only. It isn't a procedure for the high-voltage battery in a hybrid or electric car. If you don't have the correct procedure or equipment, let a suitably equipped technician do it.
After fitting: check the vehicle's 12 V charging system is working, or the new battery won't last. Signs of a charging fault
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General guidance only. Always follow your vehicle owner's manual.